1. Field of the Invention
This invention relates generally to preparations for whitening human teeth, and more particularly, to a stable, storable composition which when applied onto the surface of teeth acts to whiten and polish teeth without damage to oral tissues.
2. The Prior Art
A tooth is comprised of an inner dentin layer and an outer hard enamel layer that is the protective layer of the tooth. The enamel layer of a tooth is naturally an opaque white or slightly off-white color. It is this enamel layer that can become stained or discolored. The enamel layer of a tooth is composed of hydroxyapatite mineral crystals that create a somewhat porous surface. It is believed that this porous nature of the enamel layer is what allows staining agents and discoloring substances to permeate the enamel and discolor the tooth.
Many substances that a person confronts or comes in contact with on a daily basis can "stain" or reduce the "whiteness" of one's teeth. In particular, the foods, tobacco products and fluids such as tea and coffee that one consumes tend to stain one's teeth. These products or substances tend to accumulate on the enamel layer of the tooth and form a pellicle film over the teeth. These staining and discoloring substances can then permeate the enamel layer. This problem occurs gradually over many years, but imparts a noticeable discoloration of the enamel of one's teeth.
Dentifrices, especially toothpaste, gels and powders containing active oxygen or hydrogen peroxide liberating ingredients such as peroxides, percarbonates and perborates of alkali and alkaline earth metals or complex compounds containing hydrogen peroxide with salts of the alkali or alkaline earth metals have been disclosed in the prior art for the whitening of teeth. However, of all the peroxide compounds suggested by the prior art for whitening teeth, only two peroxide releasing compounds, urea peroxide and hydrogen peroxide, are approved by the Food and Drug Administration for use in oral compositions.
One method for whitening teeth used by dental professionals involves the use of 37% hydrogen peroxide in combination with heat and light to promote the oxidation reaction. This method, although fast, is losing favor with dentists because clinical and scientific evidence shows that high concentrations of peroxide are deleterious to oral tissues.
Another professional method for bleaching teeth involves the use of hydrogen peroxide generating compounds such as urea peroxide (carbamide peroxide) at concentrations of 10-20% to achieve the desired whitening effect. Urea peroxide rapidly breaks down into hydrogen peroxide due to the water present in saliva. This method known as an office-monitored at-home bleaching system involves the use of a mouth guard or tray within which the bleaching agent is placed. The tray is then placed upon the teeth of the patient and bleaching is allowed to take place. This method of treatment has drawbacks including tooth sensitivity, possibly due to demineralization and irritation of oral tissues. An additional disadvantage of the tray application method is that the bleaching effect is very slow.
There is a demand in the marketplace for a tooth whitening product that can be used at home or in private by the consumer and is safe and easy to use. A product for home use cannot utilize the compositions or products for whitening teeth that are available for use by a trained dental professional. For example, the 35% hydrogen peroxide bleaching agent utilized by many dental practitioners to bleach teeth is sufficiently concentrated to be irritating and potentially dangerous for home use by the consumer.
There are available in the marketplace non-abrasive dentifrice compositions for home use which contain 1-3% by weight concentrations of hydrogen peroxide and when brushed on the teeth effect whitening and removal of stains.
A drawback to home use bleaching dentifrices containing oxygen liberating bleaching compounds is the tendency of these products to decompose within a relatively short period of time following manufacture with concomitant loss of all or a substantial amount of the available oxygen thereby limiting the efficacy of these products as teeth whitening compositions. Peroxy compounds such as hydrogen peroxide are notoriously unstable with respect to maintenance of peroxide level and have been found to be difficult to formulate into aqueous gels or pastes which will have an adequate shelf-life and yet will readily liberate oxygen when applied to the oral cavity. Therefore, the prior art, for example U.S. Pat. Nos. 4,988,450 and 3,657,413 in formulating oxygen liberating compositions for the whitening of teeth utilize anhydrous powders or water-free pastes or gels which must be protected against contamination and chemical interaction. A drawback to the use of such anhydrous products is that, due to the absence of water, application of the oral composition tends to desiccate oral tissues which leads to irritation and tissue damage.
Whitening products formulated with peroxy compounds normally do not contain abrasive polishing agents as such materials activate the rapid decomposition of the peroxy compounds whereby the oxygen whitening agent is prematurely released. The gas evolution is especially undesirable with a toothpaste or gel product as such gas evolution can cause swelling and/or bursting of tubes containing same. Capped tubes filled with dentifrice products containing peroxy compounds and silica abrasives have been known to explode within one day after filling. When alumina abrasives are substituted for silica, the filled product is pocketed with gas holes within days of filling.
A drawback to the use of whitening products which are formulated without abrasives is that, in addition to having a slow bleaching action, the products are not effective in stain removal. Thus the polishing agent incorporated in a dentifrice acts to debride and physically scrub the external surface of teeth. This scrubbing action removes filmy bacterial and plaque layers as well as some of the stains and discoloring pigments that are found on teeth that cause the undesired discoloration. These polishing agents also microabrade the tooth so as to polish the teeth to give the enamel a more lustrous appearance and a higher optical sheen. This microabrasion action enhances the scrubbed teeth's ability to reflect white light and thereby appear brighter.
Illustrative of non-abrasive oral compositions containing peroxide compounds include U.S. Pat. Nos. 4,980,152; 4,839,156; 4,522,805 and 4,567,036.
U.S. Pat. No. 4,980,152 discloses a non-abrasive aqueous oral gel composition comprising about 0.5 to about 10% by weight urea peroxide and 0.01 to 2% by weight of a fluoride providing compound. The composition further includes a thickening agent such as carboxy polymethylene, a non-ionic surfactant such as Pluronic F127, alkali soluble cellulose ethers as viscosity increasing agents, potassium phosphate as a buffering agent and glycerine as a carrier and flavoring and sweetening agents.
U.S. Pat. No. 4,839,156 discloses an aqueous dental gel containing 18-25% by weight of a polyoxyethylene polypropylene block copolymer gelling agent, hydrogen peroxide, 15-40% by weight of a polyethylene glycol humectant, flavor, sweetening agent and a non-ionic surfactant as the essential ingredients.
U.S. Pat. Nos. 4,522,805 and 4,567,036 disclose a stable toothpaste to aid in controlling periodontal disease, containing an oxidizing agent such as urea peroxide which dissociates into urea and hydrogen peroxide in the oral cavity, in a paste carrier comprising an anionic detergent, sorbitol and glycerin humectant and a thickening agent such as gum tragacanth, sodium alginate or sodium carboxymethyl cellulose.
U.S. Pat. No. 4,405,599 discloses a toothpaste consisting essentially of a combination of calcium peroxide and sodium perborate oxidizing agents, dicalcium phosphate, calcium carbonate and magnesium carbonate cleaning agents, sorbitol humectant, cornstarch, cellulose gum thickening agents, and an anionic detergent. There is no indication of the effect of the toothpaste on whitening or stain removal from teeth.